This application is based on Patent Application No. 10-357333 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a near-field optical recording/reading apparatus using a probe.
2. Description of the Related Art
In recent years various ultra high density information recording methods and reading methods have been proposed which improve the information recording density of widely used magnetic disks and optical disks. Although these methods focus on the near-field optical recording art, in these methods it is important to control the gap between the optical head and the recording medium to several tens of nanometers.
Conventional gap control methods include control methods using tunnel current, air floating methods based on the air layer lubrication principle, and share force methods using piezo elements. The tunnel current method is suitable for controlling a gap range below the nanometer order. However, the tunnel current method is unsuitable for controlling gaps on the order of several tens of nanometers such as are required in the near-field optical recording art. The air floating method is widely used in magnetic disk devices, and is considered to produce gap control of several tens of nanometers. However, a relatively large interface surface is required between the optical head and the recording medium to form the air layer. For this reason, it is difficult to ensure sufficient interface surface area in an optical head provided with a sharp-tipped probe.
The share force method is a gap control method exclusively for optical head provided with a sharp-tipped probe. However, a means is required to oscillate the probe and a plurality of optical elements are required to detect the oscillation of the probe in order to detect the gap and feedback data to drive the Z-axis piezo element, thereby disadvantageously increasing the weight of the optical heat. Moreover, the recording spot is widened by the oscillation of the probe tip, thereby disadvantageously hindering high density recording.
An object of the present invention is to provide a near-field optical recording or reading apparatus capable of detecting the gap between a probe tip and a recording medium by a simple and light-weight construction.
Another object of the present invention is to provide a near-field optical recording or reading apparatus which does not produce the side effect of widening the recording spot.
These objects are attained by the near-field optical recording apparatus or reading apparatus of the present invention comprising: a driver for supporting an optical head and maintaining a gap between a recording medium and a probe; a first conductive layer covering at least the tip portion of the probe; a detector for detecting the electrostatic capacity between the first layer and a second conductive layer provided on the recording medium; and a controller for controlling the gap between the probe and the recording medium based on the detection result of the detector.
In the present invention, the gap between the probe and the recording medium is maintained at an approximately fixed gap by a driver, e.g., a Z-axis piezo element. At this time, the electrostatic capacity between the first and the second conductive layers is maintained at a fixed value. When the gap fluctuates, the electrostatic capacity changes, and the amount of this change is detected and fed back to the driver to maintain a fixed gap.
A third conductive layer may cover the first conductive layer through an insulation layer. The third conductive layer functions as a shield layer relative to electric noise and magnetic noise, and can eliminate the influences of external noise when detecting electrostatic capacity. Alternatively, the signal of the first conductive layer may be subjected to impedance conversion and the converted signal may be input to the third conductive layer so that the first and the third conductive layers have identical electric potentials. According to this construction, detection of the electrostatic capacity between the first and the second conductive layers produces a higher accuracy, and allows accurate detection of the change even in wide gaps.